Ask A Scientist Chemistry Archive

name         Frank
status       other
grade        other
location     IL

Question -   What is the difference between a technical, and a reagent 
chemical, of the same type?
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The difference is in the purity of the sample.

Greg (Roberto Gregorious)
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Reagent grade is usually purer than technical grade.
I think Technical means it is pure enough for certain uses like solvent 
cleaning or reactions to generate bulk products,
and Reagent Grade means that the impurities are reduced to a level
where you often cannot collect any unintended products due to them,
or if that is impractical, to some compromise level only slightly less 
than that.

When drying on a surface, Technical Acetone may leave more solid organic 
residue than Reagent-Grade Acetone.
It might not be a great window-cleaner; a bit "streaky".
But Technical grade is less rigorously defined than Reagent Grade,
so manufacturers are free to make their own "Technical Grade" optimized 
for whatever they want,
and a few are indeed optimized to have low solid residue on evaporation.
In such cases it is the manufacturer's job to advertise this alongside the 
grade rating.

Analytical Grade is in many senses purer than Reagent Grade,
because it means that impurities are so low that fairly sensitive 
instruments will not see much of any one of them.
It takes a much higher impurity concentration to separate and collect some,
than it does to see a subtle color-contribution in a spectrometer.
An Analytical-grade solvent might have water-content in the PPM's,
low enough that if you leave the cap off too long and it dissolves water 
vapor from the air,
that doubles or multiplies its water concentration.

Semiconductor Grade is often purer than Reagent Grade too, but it does not 
have to be.
This grade targets certain impurities which are known to be detrimental in 
making
IC- and transistor-chips, reducing them orders of magnitude, whereas
other impurities chemically similar to the main product may be quite 
acceptable in 1% levels.
Metals, as ions or soluble salts or metal-organic complexes,
are the most prominent chemical family that must be absent from liquids 
used to clean semiconductor wafers,
because they change the doping of the semiconductor.
Next most important to reduce are solid residues which might form on 
drying, diluting, or reacting,
because residues fouled up the photoresist pattern-making and get in 
between material layers.
Often that simplest way to get these classes of impurities out involves 
make a product that is very pure in other ways too.
On the other hand, 0.2% water often does not matter much in a 
Semiconductor-grade solvent.
They get dipped in clean water very often, and water is often not detrimental.

The relevant impurities in each grade are different for different chemicals.
Reading the particular manufacturer specs for specific impurity levels is 
the definite way to know.

You can see that these grades cannot necessarily be ranked in a line.
I could probably start a rousing argument with a chemist if I claimed that 
Semiconductor Grade was purer than Analytical Grade.
Each is a profile fitted to a general type of use.
But the logic of each one can rub off on you.

Jim Swenson
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